XMM-Newton Upper Limits

Upper limits, from the three EPIC cameras, have been pre-calculated and stored in a database for slew and pointed observations which are public. This is an on-going process with new observations being added as they become available. They have been calculated at 1,2 and 3-sigma significance using 1-sided Bayesian statistics, which correspond to confidence probabilities of 84.13, 97.72 and 99.87% that the true count-rate value lies below the respective upper limit.
Values are available for soft (0.2-2 keV), hard (2-12 keV) and total (0.2-12 keV) energy bands.

Conversion from count-rate to flux is dependent on the camera, on the filter used in the observation and on the assumed spectrum. Factors are given in the following table, in units of [1E11 cts cm^2/erg], for a spectrum of a power-law of slope 1.7 absorbed by a column, NH=3E20 cm^2.
The same conversion factors are used to calculate source fluxes in the 4XMM source catalogue:


Instrument Filter Energy Conversion Factor (ECF)
0.2 - 2.0 keV 2.0 - 12.0 keV 0.2 - 12.0 keV
epn open 9.6304 1.1213 4.1236
epn thin 7.3866 1.1086 3.3243
epn medium 7.0298 1.0992 3.1924
epn thick 5.4091 1.056 2.5928
emos1 open 2.3808 0.3883 1.0916
emos1 thin 1.929 0.3832 0.929
emos1 medium 1.8531 0.3797 0.900
emos1 thick 1.5301 0.3672 0.7779
emos2 open 2.3905 0.3965 1.1003
emos2 thin 1.9322 0.3919 0.9358
emos2 medium 1.8548 0.3881 0.906
emos2 thick 1.5301 0.3749 0.7829

           Flux = count-rate / ECF (erg/cm^2/s)

Upper limit records are shown when the input position lies within the field-of-view of a pointed or slew observation and is not close to a detected source, is not close to a chip gap or the edge of the field and where, for pointed observations, the background is non-zero.

Upper limits are calculated from pipeline images using aperture photometry. Source counts are extracted from a circle of radius of 15 arcseconds (pointed) and 30 arcseconds (slew). Background counts for pointed data are extracted from background maps, with a circle of radius 60 arcseconds. For slew observations, background counts are extracted from an annulus of inner radius 60 arcseconds and outer radius 120 arcseconds.

For more details of the calculation process please see https://arxiv.org/abs/2106.01687